1. Field of the Invention
This invention relates generally to a method and apparatus for routing die interconnections on a semiconductor die and, more specifically, to a method and apparatus for routing die interconnections using intermediate connection elements secured to a major surface of the die.
2. State of the Art
A typical integrated circuit (IC) or semiconductor die includes external connection points termed xe2x80x9cbond padsxe2x80x9d that are in electrical communication with integrated circuits formed in or on the active surface of the die. The bond pads are used to provide electrical connection between the integrated circuits and external devices, such as lead frames or printed circuit boards. The bond pads also provide sites for electrical testing of the die, typically by contact with probes, which send and receive signals to and from the die to evaluate the functionality of the die.
In a conventional die/lead frame assembly, the semiconductor die is attached to a die paddle of a lead frame using an adhesive or tape. The bond pads formed on the face of the die are typically electrically and mechanically attached to lead fingers terminating adjacent the periphery of the die using thin bonding wires of gold, aluminum or other metals or alloys. Other types of lead frames, such as so-called xe2x80x9cleads over chipxe2x80x9d (LOC) or xe2x80x9cleads under chipxe2x80x9d (LUC), dispense with the die paddle and support the die from portions of the lead fingers themselves.
Wire bonding is typically a process through which some or all of the bond pads formed on the face of the die are connected to the lead fingers or buses of a lead frame by thin bonding wires. The bonding wires comprise the electrical bridge between the bond pads and the leads of the packaged integrated circuit. A wire bonding apparatus bonds the bonding wires to the bond pads and to the lead fingers, typically using heat and pressure, as well as ultrasonic vibration in some instances. Following wire bonding, the lead frame and die are typically encapsulated in a plastic (particle-filled polymer) or packaged in a preformed ceramic or metal package. After encapsulation, the lead fingers are then trimmed and usually bent to form external leads of a completed semiconductor package in what is termed a xe2x80x9ctrim and formxe2x80x9d operation.
Another wire bonding application may include chip-on-board (COB), where the back-side surface of a bare IC die is directly mounted on the surface of a substantially rigid printed circuit board (PCB) or other carrier substrate, and bond pads on the front-side or active surface of the bare die are then wire bonded to wire bondable trace pads or terminals on the surface of the PCB to interconnect circuitry in the die with external circuitry through conductive traces on the PCB. Likewise, wire bondable traces may be formed from a metal film carried on a flexible polyimide or other dielectric film or sheet similar to those employed in so-called TAB (tape automated bonding) lead frame structures. A die may be back-mounted on the flex circuit and the traces wire bonded to bond pads on the surface of the die.
A typical die bond pad is formed as a rectangle or square typically having an area of less than 104 xcexcm2 and framed or bounded by a passivation layer on the face of the die. Bond pads are typically formed from a conductive metal such as aluminum and electrically connected to an underlying integrated circuit formed in or on the die. Usually a barrier layer and a polysilicon layer separate the bonding pad from an oxide layer of a silicon substrate in which the active semiconductor devices are formed. A passivation layer formed of a dielectric material (silicon dioxide, silicon nitride, polyimide, BPSG, etc.) or as a sandwich of different materials (e.g., silicon dioxide/silicon) covers the oxide layer, and the bond pad is embedded in the passivation layer. Such bond pads may be located generally along the peripheral edges of the die, inset from the edges a desired distance, or in one or more center rows. These bond pads are then typically wire bonded to a lead frame, thermocompression bonded to an overlying TAB tape or flip-chip bonded (with appropriate prior xe2x80x9cbumpingxe2x80x9d of the bond pads) to a printed circuit board.
It is often desirable to interconnect various bond pads on a single semiconductor die in order to alter the input and/or output functionality of the die, such as when it is necessary to xe2x80x9cwire aroundxe2x80x9d defective portions of a die which is only partially functional. For example, a 16 megabit DRAM memory die may only demonstrate 11 megabits of functional memory under electrical testing and burn-in. Alternatively, it may be desirable for a die having a given input/output (bond pad) configuration to xe2x80x9clookxe2x80x9d to a particular lead frame or carrier substrate as if it were configured differently so that the die could be used with a lead frame for which it was not originally intended. Such xe2x80x9cwire aroundxe2x80x9d functions, where possible, are typically accomplished by interconnecting bond pads on the die through external circuitry in printed circuit boards or other carrier substrates to which the die is mounted. Where the desired input and/or output functionality configuration varies from die to die, a separately configured printed circuit board or other carrier substrate must be provided for each desired input and/or output functional configuration. Thus, it would be desirable to provide a relatively easy way of interconnecting selected bond pads on a single integrated circuit die without requiring the use of external circuitry in printed circuit boards and other carrier substrates.
Accordingly, a semiconductor die according to the present invention is comprised of a die bearing integrated circuits. Such integrated circuits may comprise a memory device, microprocessor, or any other semiconductor device or functional combination of devices. In a preferred embodiment, the active surface of the die (i.e., the surface of the die having bond pads thereon and bearing the integrated circuits) includes at least one electrically isolated intermediate connection element or wire-bondable jumper pad attached thereto, each bondable jumper pad being electrically isolated from external circuitry and from circuitry of the die, but for wire bonds extending to and/or from the bondable jumper pad. That is, each bondable jumper pad is not directly electrically connected to internal circuitry of the die, unlike the bond pads, but provides a xe2x80x9cstepping stonexe2x80x9d for wire bonds between bond pads of the die or between a bond pad and a conductor external to the die. Thus, a relatively short wire bond can be formed from a bond pad to the jumper pad and another relatively short wire bond formed from the jumper pad to another bond pad (or external conductor) forming an electrical connection between the two bond pads (or bond pad and external conductor).
In another preferred embodiment, a plurality of jumper pads is provided over the active surface of the die, providing various serial jump points for a plurality of wire bonds to be formed in series between a plurality of bond pads. Where the semiconductor die has bond pads located about a peripheral edge of the active surface, a grid or array of jumper pads may be provided proximate the center of the active surface and at least partially bounded by the peripheral bond pads.
In yet another preferred embodiment, the semiconductor device is of the aforementioned LOC configuration and includes a lead frame having lead fingers and/or bus bars that extend over the active surface of the die. In addition, a plurality of jumper pads is provided on the active surface so that wire bonds can be made from bond pads to jumper pads to bus bar to jumper pad to bond pad to lead finger, or any combination thereof, depending on the desired input/output (I/O) configuration of the die.
Preferably, the jumper pads are comprised of a conductive material, such as metals (e.g., aluminum or gold) or alloys thereof.
In a preferred embodiment, the jumper pads are silk-screened onto the active surface of the die. The jumper pads may also be electrolessly plated, electroplated, or electrochemically deposited, printed, sprayed (through a mesh), adhesively attached or otherwise formed onto the active surface of the die.
In yet another preferred embodiment, the jumper pads are formed in a grid or array on one side of an adhesive tape or film. Such a tape or film could then be cut to size to fit the specific die. The tape could be attached to the die by thermosetting, application of pressure, or other methods, depending on the type of tape and adhesive employed.
In another preferred embodiment, the jumper pads may be formed over a segment of insulating or dielectric material, such as a nonconductive film or coating, that is applied to the active surface of the die. The insulating material protects internal circuitry near the active surface from any interference or shorting that may be otherwise generated by the presence of the jumper pad or connections to the jumper pads.
In yet another preferred embodiment, a jumper pad adapter is attached to the active surface of the die by an adhesive. The adhesive may be a pressure sensitive adhesive, a thermosetting adhesive or any other suitable adhesives known in the art. The jumper pad adapter includes a plurality of conductive lines extending through the adapter from the lower surface thereof which provides electrical contact between the bond pads or conductive bumps formed on the die and contact pads formed on the top surface of the jumper pad adapter. Thus, jumper pads are formed on the upper surface of the adapter rather than on the active surface of the die, and the contact pads and jumper pads on the adapter lie in substantially the same plane. Accordingly, all wire bonds between jumper pads and contact pads can be formed in the same horizontal plane relative to the top surface of the jumper pad adapter.
Preferably, the jumper pad adapter includes access holes that extend through the adapter to allow access for wire bonds to be made to bond pads on the active surface of the die that would otherwise be covered by the adapter.
In another preferred embodiment of the jumper pad adapter, the adapter includes internal and/or external conductive paths which can route signals between jumper pads and to and between bond pads on the active surface of the die.
In yet another preferred embodiment, an adapter, which converts a die having peripherally mounted bond pads to a flip-chip array connection configuration, includes first contact pads electrically connected to the bond pads of the die, second contact pads exposed on the top of the adapter and in horizontally-offset locations from the bond pads, and conductors extending to and between the first and second contact pads. The second contact pads may be bumped so that the adapter, and thus the die, can be flip-chip bonded to a PCB or other carrier substrate.